There is a few things you could try on the walls if the pictures aren't too heavy.
There is a blue tacky stuff that I originally used to put post cards on my cabinet doors. Only problem is that
it might stain your ensolite (?).
POSTER PUTTY
The postcards are so
light weight that I have found that a
CANDLE ADHESIVE works really well. It's made to hold candles upright. Since it's clear, there shouldn't be a staining issue. In fact, it does a better job than the putty on my postcards.
I also ran across
THIS STUFF I've never used it, but it looks promising.
There is also something out there called
GLUE DOTS that looks very promising. Not sure if it would damage the ensolite or not.